Synergistic Effect of In-Situ Al-7075/Al3Ti Metal Matrix Composites Prepared via Stir-Assisted Ultrasonic Melt Processing Under Dynamic Nucleation

Abstract

Owing to the high propensity for particle agglomeration, the fabrication of aluminum matrix composites with uniform distribution using casting routes is extremely difficult. In this study, the in-situ development of the Al3Ti reinforcing phase by employing stir-assisted ultrasonic treatment was utilized to improve the homogeneity, wettability, and thermodynamic stability of the reinforcing particles in an Al-7075 alloy matrix. The in-situ Al3Ti particles acted as heterogeneous nucleation sites and facilitated grain refinement to form a non-dendritic globular structure compared with the dendritic cells of the base alloy. The grain size of the alpha-Al dendrites reduced from 160 mu m to 65, 50, and 40 mu m with the addition of 2, 5, and 7 wt% Al3Ti, respectively. The reduction in the porosity of the composites and the improvement of the particle homogenization were due to cavitation-induced de-agglomeration and the degassing effect. The formation of a robust and clean interface between the Al3Ti particles and Al alloy via ultrasonic vibration improved the integrity of the composites compared with that of the base alloy. The thermal expansion mismatch between the Al3Ti particles and Al alloy contributed significantly to the improved mechanical properties of the composites.